Apparatus for the extrusion of metal



Aug 18, 1%6. P. DUNSHEATH l 7 2,051,

' APPARATUS FOR THE EXTRUSION OF METAL Filed Feb. 13, 1933 4 2Sheets-Sheet 1 a uvvzwraxe Ivy JQQATTOR/VEXS Aug 1%, 1936. P. DUNSHEATH2,051,683

APPARATUS FOR THE EXTRUSION OF METAL Filed Feb. 15, 1953 2 Sheets-Sheet2 Z1, ATTORNEYS Patented Aug. 18, 1936 JPATENT OFFICE Percy Dunsheath,Kent, England, assignor to T. Henleys Telegraph Works Company Limited,London, England, a British company Application February 13, 1933, SerialNo. 656,498 In Great Britain March 5, 1932 19 Claims. (Cl. 207 2) Thisinvention relates to the extrusion of metal by a method employing arotating screw-threaded impelling device by which the metal is drivenforward in the extrusion chamber to and through the die, or between aninner die and an outer die. The impelling device comprises twolongitudinally extending concentric members of forms which arein'general circular in cross section. Thesemembers have on theiradjacent faces projections.

and/or recesses which are adapted to engage metal placed in the spacebetween the members.

The metal in the molten state is fed into one end fed forward by ascrewing action. Continuousrotary movement of the impelling devicecombined with continuous feeding of molten metal results in continuousdelivery of metal in the solid state to the extrusion chamber and inextrusion of it by the pressure exerted on it by the following metal. I

It will be seen that the method of working imposes certain limitationson the metals to which it is applicable. It is particularly useful inconnection with lead and lead alloys and in extrusion in the form ofpipes or as sheaths on electric cables.

.The apparatus may conveniently be formed'as a long annular chamber intoone end of which the molten metal is fed by gravity, and from the otherend of which the metal is extruded. The two endssof this chamber may befixed and the central portion maybe formed by the outer part of thescrew threaded impelling device. The inner member of the impellingdevice may extend through the whole length of the chamber and carry aninner die (when this is required) at the extrusion end. This willco-operate with the outer die carried by the end of the chamber inproviding an annular space of appropriate form and dimensions for thepassage of the extruded metal. This inner member may be hollow to servefor the passage of an electric cable when the machine is being used forsheathing cables.

Hitherto in apparatus of this kind one of the members of the impellingdevice has been stationary and its efiectivesurfaces have been formed soas to guide the metal parallel with These surthe axis, and restrain itfrom following the rotary movement of the other member, which has beenprovided with screw-threads. For this purpose the stationary. part hasbeen given ribs or flutes running parallel with the axis of the machine.It is the object of the present invention to increase the efliciency ofoperation of such apparatus by reducing the proportion of the suppliedenergy which is wasted by the friction between the metal which is beingextruded and the two members of the impelling device and by the internalfriction of the metal itself resulting from the application of excessiveshearing forces to it by the two members of the impelling device aspreviously constructed. In accordance with the present invention bothmembers of the impelling device are provided with surfaces such asthreads, ribs or flutes which are inclined in helical form. These aredisposed in opposite senses on the two members. On producing relativerotation between the two members the effective helical surfaces of bothof them impart to the metal between them an endwise thrust.

In general, one of the members carrying the helical driving surfaceswill be stationary, but it is within the scope of the invention to makeboth members to rotate, the rotations being in opposite senses. threadsof approximately equal pitch and are given approximately equal rates ofrotation they may cause the metal to travel along the extrusion chamberwithout rotation about the axis. Ifone .of the members is fixed and theother rotates the metal will receive a rotation as well as an endwisemovement. i

.The invention will be further described by the aid of the accompanyingdrawings of which Figure 1 shows a longitudinal section of parts of anextrusion apparatus embodying the invention and Figure 2 shows analternative form of inner member. It is to be understood that Figure 1,as regards the general construction of the machine, is to a large extentdiagrammatic. It shows the relative disposition of the important partsof the machine, but is not intended to indicate the details of theirconstruction.

In this example the rotary part of the impelling device is the outertubular member I. It is carried by bearings in the frame 3 and is drivenby the wheel 4. It makes a running joint at the inlet end with the wallof the feeding chamber 2 and also makes arunning joint at the deliveryend with the wall of the extrusion chamber 5.

In this case if both members have' The inner member 6 of the impellingdevice is I and is supported at the front end in a ring 8 forming partof a spider 9. It carries at its front end the inner die III whichcooperates with the outer die II.

The lower part of the frame: 3 and its contents have been omitted astheir presence is unnecessary for an understanding of the presentinvention. On similar grounds the means for fixing the outer die andother details are not shown.

In the operation of the machine molten metal is continuously fed intothe chamber 2 and flows into the spacebetween the two members, I and 6,of the impelling device. It is there cooled to a sufficient extenttobecome plastic and to be engaged by the threads of these members. Itwould be noted that, as previously mentioned, the threads are ofopposite hands, that on the member I being right-handed and that on themetal against the threads of the member 6 and the reaction of thesethreads on the metal assists to force it forward. As a result of theseactions the metal is delivered into the extrusion chamber 5 and forcedout through the space between the dies l0 and II. The member 6 isprovided with a central passage I3 through which can be inserted anelectric cable when the extrusion apparatus is to be employed forapplying a lead sheath to a cable.

The advantageous results of giving a helical formation to the efiectivesurfaces on the second of the two concentric members instead of makingthem parallel to the axis are at least of two kinds. The stress to whichthe metal is subjected by the combined actions of the effective surfacesof the two members is materially decreased and the frictional losses, indriving the metal through the chamber, are reduced. The stress producedin the metal isdue to a tendency to shear that part of the metal, whichis directly acted upon by the effective surfaces of one of theconcentric members, over that part of the metal which is acted upon bythe effective surfaces of the other member. The surfaces on which thisshear tends to take placeis a cylinder or cone lying between the twoconcentric members. In the example illustrated there is a tendency tocause the metal, which lies between the threads of the outer member I,to slide over the metal which lies between the threads of the innermember 6. The surface of shear isaccordingly a cylinder enveloping thethreads of the member 6 and lying within the threads of the member I.From the nature of the metal being dealt with and the fact that it is ata comparatively high temperature, it follows that the metal cannotpossess high resistance to shear. It is therefore important for theefiicient working of the machine that the tendency to shear should bekept low. It appears doubtful whether shearing can be entirely preventedsince the material which is being impelled is rather of the nature of ahighly viscous liquid than of the nature of a solid, but it is obviousthat it is desirable to keep the shearing movement as small as possible.i The inclination of the effective surfaces of the second member of theimpelling device, so as to make them helical instead of parallel withthe axis, greatly reduces the tendency to shear. In practice it hasbeenfound that it has the effect both of reducing the slip between thethreads and the metal and of reducing the .power absorbed by the machinefor a given outproximately the same in both the inner and outer member.It appears that this angle can advantageously be made 70 and upwards.

As indicated in the preceding description the effect of the inclinationof the operative surfaces of the second member is to facilitate therotation of the metal about the axis of the machine as it travelsforward. This rotation in general should not continue up to the point ofextrusion. It can be restrained by the engagement of the metal in theextrusion chamber with the stationary end wall. Additional restraint canbe provided by stationary surfaces projecting into that chamber. In theexample illustrated such surfaces are provided by the legs of the spider9. These legs may be provided with surfaces which, at the sideat whichthe metal comes to them from the impelling device, are inclined so as tobe'substantially parallel with the direction of movement of the metalleaving that device and are then curved so as to divert the movement ofthe metal from a helical movement into a movement parallel with theaxis. In many cases however this inclination and curvature will not benecessary.

As an alternative means of restraining the effect of the rotarycomponent of the movement of the metal, near the extrusion end of thechamber, the operative surfaces on the stationary member of theimpelling device may be made substantially parallel with the axis atthat end. This involves a change of the angle of the inclination ofthese surfaces which may be continuous over a considerable lengththereof or may take place mainly at the delivery end. The latter appearsto be the preferable arrangementand is illustrated in Figure 2 where thethreads I6 increase in pitch in the course of the last turn. Thisformation of the stationary thread may be combined with a change in theinclination of the thread on the rotary member of which the pitchdecreases as the pitch on the stationary member increases. Alternativelythe threads on the rotary member may terminate at a short distance awayfrom the delivery end as shown in Figure 1.

What I claim as' my invention and desire to secure by Letters Patent is;

1. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means for producingrelative rotary motion between said members, said members being providedon their adjacent faces with substantially continuous surfaces inclinedin helical form round the axis-of rotation, the inclination on the outermember being in opposite sense to that of the inner member and positivemeans for preventing the rotation of the metal, the said means acting onthe metal after it leaves the impelling device.

2. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means for fixing one ofthese members in position, and means for rotating the other of thesemembers, the twomembers being provided on their adjacent faces withsurfaces inclined in helical form about the axis of rotation, theinclination on the fixed member being of opposite sense to that on therotary member and the pitch of the helical surfaces of the stationarymember being gradually increased at the delivery end so that the finalpart of it is approximately parallel with the axis.

3. A rotary impelling device for the extrusion of metal, comprising twocylindrical members located one within the other, means for fixing oneof these members, means for rotating the other of these members, screwthreads projecting from the adjacent faces of the two members, thethread on the outer member being of opposite hand to that on the innermember, means for feeding molten metal into the one end of the spacebetween the two members, a chamber receiving the metal delivered inplastic form from theother end of the said space, stationary projectionsin said chamber engaging the metal'as. it passes through the chamber,and a die mounted in said chamber and providing an outlet for theextruded metal.

4. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means for producingrelative rotary motion between said members, said molten metal, meansfor producing relative rotary motion between said members, said membersbeing provided on' their adjacent faces from the point of introductionof the molten metal toa point adjacent the opposite ends of said memberswith continuous surfaces inclined in helical form round the axis ofrotation, the inclination on the outer member being'in opposite sense tothat of :the inner member whereby to minimize shearing and chopping ofthe metal between the point of introduction and the point of dischargeat the opposite ends of said members;

6. A rotary impelling device for the extrusion of metal,- comprising twolongitudinally extending concentric members, means adjacent one end ofsaid members for the introduction of molten metal, means 'for'producingrelative rotary motion between said members, said members being providedon their adjacent faces from the point.

of introduction of the molten metal to a point adjacent the oppositeends of said members with continuous surfaces inclined in helical formround the axis of rotation, the inclination on the outer member being inopposite-sense to that of the inner member and the twohelices being ofapproximately equal pitch, whereby to minimize shearing andchopping ofthe metal between the point of introduction and the point of dischargeat the opposite ends of said members.

'7. A rotary impelling device for the extrusion of metal tubes,comprising two longitudinally extending concentric members, an extrusionchamber adjoining the ends of said members, an extrusion die in the wallof said chamber on-the delivery side thereof, a seconddie mounted on theend'of the inner longitudinally extending member, and means for rotatingthe outer longitudinally extending member, said members for at leastthemajor portion of their lengths being provided on their adjacent faceswith substantially continuous surfaces inclined in helical form roundcomprising two longitudinally exthe axis of rotation, the inclination onthe outer member being in opposite sense to that of the inner member.

8. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means for producingrelative rotary motion between said members, said members for at leastthe major portion of their lengths being provided on their adjacentfaces with substantially continuous surfaces inclined in helical formround the axis of rotation, the inclination on the outer member being inopposite sense to that on the inner member, and the in- ,clination ofone of said members being at least seventy degrees to a line parallelwith the axis.

9. A rotary impelling device for the extrusion of metal comprising twolongitudinally extending concentric members, means for producingrelative rotary motion between said members, said members being providedon their adjacent faces with substantially continuous projectionsinclined in helical form round the axis of rotation, the inclination onthe outer member being in opposite sense to that on the inner member,the inner edges of the. said projections on the outer member and theouter edges of the said projections on the inner member each lyingsubstantially in a cylindrical surface over the major part of the lengthof said projections.

' 10. A rotary impelling device for the extrusion of metal comprisingtwo longitudinally extending concentric members, means for producingrelative rotary motion between said members, said members being providedon their; adjacent faces with substantially continuous projectionsinclined in helical form round the axis of rotation, the inclination-onthe outer member being in opposite sense to that on the inner member,the inner edges of the saidprojections on the outer member and l theouter edges of the said projections on the inner member each lyingsubstantially in a cylindrical surface over the major part of the lengthof said projections and these cylindrical surfaces being nearlycoincident.

11. A rotary impelling device for the extrustion of metal. comprisingtwo longitudinally extending concentric members, one being stationaryand the other rotary, and means for producing rotary movement of thelatter member, both said members being provided on their adjacent faceswith substantially continuous projectionsinclin'ed inhelical form roundthe axis of rotation, the inclination on the stationary member being inopposite sense to that on the rotary member and the projections on thestationary member having their edges lying on a cylindrical surface, atleast over the major part of the length of said member.

12. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means forproducing relativerotary motion between said members, said members being provided on theiradjacent faces with substantially continuous projections inclined inhelical form round the axis of rotation, the inclination on the outermembenbeing in opposite sense to that on the inner member, the pitchesof the helices being equal at least over a substantial portion of thelength of the said members near the end at which metal is fed thereto,the inner edges of the saidprojections on the outer member and the outeredges of the said pro jections on the inner member each lyingsubstantially in a cylindrical surface over the major part of the lengthof said projections.

13. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members, means for fixing one ofthese members in position, and means for rotating the other of thesemembers, the two members being provided on their adjacent faces withsubstantially continuous surfaces inclined in helical form about theaxis of rotation, the inclination on the fixed member being of oppositesense to that on the rotary member and the pitch of the helical surfacesof the stationary member being increased gradually in the final turn atthe delivery end.

14. A rotary impelling device for the extrusion of metal, comprising twocylindrical members located one within the other, means for fixing oneof these members, means for rotating the other of these members, screwthreads projecting from the adjacent faces of the two members, thethread on the outer member being of opposite hand to that on the innermember, means for feeding molten metal into the one end of the spacebetween the two members, a chamber receiving the metal delivered inplastic form from the other end of the said space, a spider in saidchamber supporting the end of the inner cylindrical member and engagingthe metal as it passes through the chamber and a die mounted in saidchamber and providing an outlet for the extruded metal.

15. A rotary impelling device for the extrusion of metal, comprising twolongitudinally extending concentric members having on their adjacentsurfaces helical projections running in opposite senses on the twomembers, means for feeding molten metal into the space between the saidmembers to keep this space completelyv filled with metal whichsolidifies therein, and rotary driving means applied to said members andproducing continuous feeding forward of solidified m'etal by thecombined and cooperative actions of the inner and outer sets of helicalprojections engaging therewith; v

16. A rotary impelling device for the extrusion of metal, comprising twolongitudinally ex-' tending concentric members having on their adjacentfaces helical surfaces, the helix on the outer member being of oppositesense to that on the inner member, means for producing relative ,ofmetal, comprising two longitudinally extending concentric members, meansfor fixing one of these members in position and means for rotating theother of these members, the two members being provided on their adjacentfaces with surfaces inclined in helical form about the axis of rotation,the inclination on the fixed member being of opposite sense to that onthe rotary member and the fixed member having at the delivery end atleast one projecting surface which is substantially parallel with theaxis.

18. A rotary impelling device for the extrusion of metal comprising twolongitudinally extending concentric members, an extrusion chamberlocated beyond the end of said members and receiving metal therefrom, adie in the delivery side of said chamber and means for producingrelative rotary motion between said members, said members being providedon their adjacent faces for at least the major portion of their lengthswith substantially continuous surfaces inclined in ceiving metaltherefrom, a die in the delivery side of said chamber, means forproducing relative rotary motion between said members, said membersbeing provided on their adjacent faces for at least the major portioh oftheir length with substantially continuous surfaces inclined in helicalform round the axis of rotation, the inclination on th outermember beingin opposite sense to that of t inner member and the two helices being ofapproximately equal pitch.

PERCY DUNSHEATH.

